A new study from Cancer Care Ontario has found no association between long-term use of antidepressants and risk for non-Hodgkin’s lymphoma. Previous animal and observational studies have shown that there may be an association between non-Hodgkin’s lymphoma and antidepressants. Based on these findings and together with the increase in rates of non-Hodgkin’s lymphoma and the use of antidepressants, Cancer Care Ontario (CCO) researchers investigated this relationship using a population-based case-control approach. They found no association between the use of antidepressants and non-Hodgkin’s lymphoma.

“While our study found no association, future studies may consider investigating individual antidepressants, especially those in the selective serotonin reuptake inhibitor (SSRI) class,” said Saira Bahl, a researcher with Cancer Care Ontario’s division of preventive oncology. “SSRIs have now been on the market for more than 10 years and researchers will have a larger pool of people exposed to this class than was available in our study.”

Cancer Care Ontario (CCO) researchers investigated the effect of antidepressant medication by comparing 638 Ontarians diagnosed with non-Hodgkin’s lymphoma (cases) to 1,930 individuals randomly selected from the Ontario population (controls). Participants completed a self-administered questionnaire that asked about use of anti-depressants and other potential cancer risk factors.

While the CCO researchers found no association between antidepressant use and non-Hodgkin’s lymphoma, they found the case subjects were more likely to consume high levels of dietary fat, were more likely to be previous smokers and less likely to be current smokers. Consistent with other studies, the researchers also found that chemical exposures are associated with increased risk for non-Hodgkin’s lymphoma. However, this can only explain some of the overall rise in this disease.

To date, research into some of the risk factors – including dietary fat, vegetable and fruit intake, alcohol consumption and smoking – has shown weak or inconsistent associations with this cancer. Viruses, such as Epstein-Barr and HIV, and immunosuppression related to organ transplantation explain only small proportions of the increase in this cancer.

“The changes in non-Hodgkin’s lymphoma over the past few decades are perplexing, in that, this cancer went from a relatively rare disease to one of the most common cancers in Ontario with little to no risk factor information to explain the dramatic change,” Bahl said. As a result, researchers feel that attention must be directed toward other potential risk factors.

In Ontario, non-Hodgkin’s lymphoma represents the fifth most common cancer diagnosed in men and the sixth most common in women. Very little is known about the causes of this disease.

This study is published in the current issue of the American Journal of Epidemiology.